Electrical safety device

ABSTRACT

A solenoid coil is connected to be energized by current through a ground wire in an electric plug. The solenoid plunger axial movement is converted to rotary step movement of an actuator which controls the operation of switch contacts connecting the power cord to the plug prongs. Power to the cord is interrupted when current flows through the ground wire. The contacts may be reset by manually moving the solenoid plunger or may be electrically reset by an external power supply to the solenoid.

United States Patent 11 1 1111 3,873,951 Blake Mar. 25, 1975 [54] ELECTRICAL SAFE TY DEVICE 3,632,23 22/1372 Cooielr. 317/18 R 3 t 3 2 [76] 11w6m6r; William s. Blake, 12802 Taylor St., 7 H 74 7 Garden Grove Cahf 92020 Primary Examiner-Harold Broome [22] Filed: Oct. 29, 1973 Attorney, Agent, or Firm-Knobbe, Martens, Olson, 21 Appl. No.: 410,373 Hubbard Bear 57 ABSTRACT [52] US. Cl 335/164, 3l7/18, 335/18, 1

335/138 A solenold c011 1s connected to be energ1zed by current through a ground wire in an electric plug. The so- [Sl] Int. Cl. HOlh 51/08 1 l Id [58] Field Of Search 335/164, 165, 166, 186, F P 2931 8 f g 335/123, 140, 138, 1, 2,18, 255; 317/18 step movement 0 an actuator w 1c contros t e 0peratlon of swltch contacts connectmg the power cord to the plug prongs. Power to the cord is interrupted [56] References Cited when current flows through the ground wire. The UNITED STATES PATENTS contacts may be reset by manually moving the sole- 3r34o-433 9/1967 Almqulsl 317/18 R noid plunger or may be electrically reset by an exterggizlg nal power supply to the solenoid. 3:562:588 2/1971 Zielasko 3l7/l8 A 10 Claims, 10 Drawing Figures ELECTRICAL SAFETY DEVICE This invention relates to electrical safety devices and more particularly to an improved safety plug which interrupts the current through a power cord whenever current flows through a ground wire.

There are many prior art safety devices designed to protect the operator of an electrical appliance or similar equipment in the event of shock or danger from a shorted out appliance. However, it appears that all these prior art arrangements have various shortcomings. Some devices energize a warning light that a dangerous situation exists, but the actual danger is not eliminated. Other devices may be temporarily rendered harmless but then have some kind of recovery arrangement so that the device can be once more reused. Yet other devices suffer from being relatively expensive or unreliable. Accordingly a need appears to still exist for an inexpensive, highly reliable safety device for protecting the operator of an applicance or other equipment in the event ofa short circuit. In accordance with a preferred form of the present invention a conventional three prong power plug is to be replaced by a plug having combined therewith a solenoid operated switch. Alternatively, the safety device may be made as a separate unit which is designed to plug into a wall outlet and receive a conventional three pronged plug. If replacing a conventional plug, three flexible switch contacts are provided within a housing for connecting the three prongs of a plug to the three wires of a power cord. A solenoid coil positioned in the housing is connected to be energized by current flowing through the ground wire and ground plug prong. Energization of the solenoid will immediately open the switch contacts so that no current can flow through any of the wires in the power cord. After the condition which caused power to flow through the ground line has been corrected so that it is desirable to once more use the plug, the solenoid plunger can be once more actuated, either manually or electrically from an external source, to close the switch contacts once more.

The switch actuating mechanism includes means for converting the axial movement of the solenoid plunger into combined axial and step-like rotational movement of a contact actuator. In a preferred form of the invention, this motion conversion is accomplished by utilizing cam surfaces on the ends of mating ribs of axially moving elements, guided by ribs on a fixed housing, to move the actuator into switch closing or opening positions.

For a more thorough understanding of the invention, refer to the following detailed description and drawings in which:

FIG. I is a perspective view of the exterior of the I safety plug of the invention;

FIG. 2 is a cross-sectional view through the plug showing the switch contacts in the open position;

FIG. 3 is an exploded perspective view of the internal components of the plug;

FIG. 4 is a cross-sectional view of the plug on line 44 of FIG. 2'illustrating the relationship between the switch contacts and the ends of plug prongs;

FIG. 5 is a cross-sectional view on line 5-5 of FIG. 2 showing the relation between the structure ribs and the guide slots;

FIG. 6 is a cross-sectional view on line 6-6 of FIG. 2 illustrating the relation of the slider to the guide;

FIG. 7 is a cross-sectional view similar to that of FIG. 2 only showing the components with the switch contacts closed;

FIG. 8 is a cross-sectional view on line 88 of FIG. 7 showing the relation of the contacts to the actuator; and

FIGS. 9 and 10 are schematic, developmental views showing the ribs and grooves of the actuator, the slider and the guide in the open and closed positions of the switch contacts.

Referring now to FIGS. 1, 2 and 3, the safety plug of the invention includes a generally cylindrical housing 10 suitably closed on one end by a retainer plate 12 which fits within the open end of the housing 10. The other end is closedv by a cover 14 which fits over the end of the housing 10. Extending through and supported by the retainer plate 12 are a ground plug prong 16, a hot plug prong 17, and a common prong I8. Electrical conductors or feeder bars 20, 21 and 22 are circumferentially spaced within the housing, extending axially adjacent the outer wall of the housing. As can be seen from FIG. 2, the feeder bars extend through a support wall 10a in the central portion of the housing and are thereby properly oriented withe other structure supported in the housing which cooperates with the feeder bars. Attached to and extending inwardly from the upper end of each of the feeder bars is a flexible contact arm 24 having positioned on its inner end a contact 24a.

The contacts are circumferentially spaced to be aligned with the inner end of a respective one of the plug prongs 16, 17, and 18. This may be easily seen in FIG. 2 for the ground prong 16.

A solenoid coil26 is positioned within an inner cylindrical housing 28 formed in the lower portion of the main housing 10, spaced inwardly from the housing 10 and formed integral with the support wall 10a of the housing. Extending through the cover 14 is a conventional three wire power cord 30 having its hot and common wires connected respectively to the lower ends of the hot and common feeder bars 21 and 22. The common wire 31 may be seen in the lower portion of FIG. 2. The ground wire 32 of the cord 30 is connected to the solenoid coil 26, with the other end of the solenoid coil being connected to the lower end of the ground feeder bar 20 by conductor 33. In other words, the solenoid coil 26 is serially connected in the ground line. A conventional solenoid core or plunger 34 is slidably positioned within the coil 26 insulated from the coil.

A reset button 66 extends through the cover 14 on the lower end of the plug housing and into the core of the solenoid coil 26 where it engages the lower end of the solenoid plunger 34. The cover 14 is formed with an upwardly or inwardly extending socket 68 which interferes with the lower surface of the cap 66a on the inner end of the reset button, thus retaining the reset button within the housing.

Positioned within the upper portion of the housing 10 is a mechanical mechanism cooperating with the plunger 34 for actuating the switch contacts 240. An inner cylindrical wall 38 is attached to and formed integrally with the housing 10. As can be seen, the wall 38 extends upwardly from the housing wall 10a and terminates at the point where the flexible contact arms 24 extend inwardly from the feeder bars 20, 21 and 22.

Spaced further inwardly is a tubular guide 40 formed integral with and extending upward from the housing wall 10a. As can be seen, the lower end of the guide 40 is open to the solenoid plunger, while the-upper end is open and terminates spaced from the contacts 24a and the plug prongs.

The movable elements of the contact acutating mechanism include a slider 42, an actuator 46, a positioning pin 44, and a cylindrical coil spring 48. These components will be described in greater detail after further description of the tubular guide 40.

Referring to FIGS. 5 and 6 as well as FIGS. 2 and 3, the tubular guide has six ribs 50 which are equally spaced around the inner periphery of the guide 40. These ribs extend from the lower end of the guide 40 and terminates near the upper end with upper surfaces 50a which are angled with respect to a plane perpendicular to the axis of the housing, such as the plane defined by the housing wall la. These end surfaces 50a form cams, which will be later discussed in more detail.

As can be seen from FIGS. and 6, the ribs extend circumferentially about 35 and define six equally spaced grooves. Three of these grooves 52 extend axialy the length of the guide 40 and extend radially the full depth of the ribs 50. The other three grooves 54 are shallower in depth. Since the grooves 54 are not as deep as the grooves 52 there is end structure 54a forming the bottom or outer wall of the groove 54 which extends radially inwardly from the circle defined by the bottom of the grooves 52. This end structure terminates spaced from the upper end of the guide and formed at an angle the same as the end of the ribs 50. Thus, this end structure 54a forms a cam surface which is the continuation of the cam 50a on the ribs which are positioned to the left or in a counter-clockwise direction, as viewed in FIG. 5. The right side or clockwise side of the cam surface 54a is bounded by a rib 50, also; however, this is the high side of the cam surface 50a for such ribs. This structure may perhaps best be seen by reference to the development view of FIG. 10.

The slider 42 has a lower tubular portion which is adapted to engage the upper end of the solenoid plunger 34. The upper end of the slider has a slightly larger tubular diameter with a series of six axially extending ribs 42b, equally spaced on the outer periphery of the slider. The circumferential width of the ribs 42b is sized so that they will slide easily within the grooves 52 and 54 of the guide 40, as may be seen in FIG. 6.

Note that the radial dimension of the ribs 42b is such that the ribs will fit within the shallow grooves 54 as well as the full grooves 52. The upper ends of the ribs 42b, as seen in FIG. 3, taper to a rounded point with the slope of the end surfaces 42c being approximately equal to the slope of the cam surfaces 50a and 54a on the ribs 50 and the end structure for the shallow grooves 54. This maybe more easily seen from FIGS. 9 and 10.

The contact actuator 46 includes a lower tubular core 46a sized to fit within the guide 40. The pin 44 extending through the center of the actuator 46 helps position the actuator 46 with respect to the slider 42. On the outer periphhery of the core 46a are three outwardly extending ribs 46b which are equally spaced circumferentially. The ribs are sized to fit within the grooves 52 in the guide 40 as may be seen in FIG. 5. It should be noted that the radial dimension of the ribs 46b is greater than that of the grooves 54 so that the lower ends of the ribs 46b interfere with the cam surfaces 54a if they are aligned with these cam surfaces.

The lower ends of the actuator ribs 46b terminate with an angular cam surface 460 which is the same as the cam surfaces 50a and 54a on the guide 40.

The upper portion of the actuator 46 includes anoutwardly extending circular flange 58 sized to fit within the cylindrical wall 38 of the housing 10. The lower surface of the flange 58 has an annular groove 58a which mates with the rounded upper edge of the guide 40 which may be seen in FIG. 2. The central portion of the upper side of the flange 58 includes walls defining a socket 60 opening upwardly to receive the lower end of the coil spring 48. The upper end of the coil spring 48 engages the inner surface of the retainer plate 12, the spring beingpositioned by a depending nipple 12a.

Formed on the outer portion of the upper surface of the flange 58 are three ramps 62, as best seen in FIGS. 2 and 3. The ramps extend circumferentially for 60 and are separated by 60 flats 63. The axial length or height of the ramps smoothly increases in a clockwise direction as viewed in FIG. 3, from a minimum to a maximum axial dimension. As may be seen from FIGS. 2 and 7 the ramps are radially and axially aligned with the flexible contact arms 24. The feeder bars 20, 21 and 22 and hence the contact arms 24 must be properly oriented with the ribs and grooves of the guide 40 to insure proper alignment of the actuator ramps with the contact arms. The ramps may also be seen in the schematic developmental views of FIGS. 9 and 10, although it should be understood that the angle or slope of the ramps 62 is more gradual than that shown in FIGS. 9 and 10. This is because the ramps are shown in FIGS. 9 and 10 as being in the same plane as the cam surfaces on the guide and the slider whereas in actuality the ramps are of course spaced outwardly from these other elements. The ramp angle is more accurately illustrated in FIGS. 2 and 3.

OPERATION The safety device of the invention is shown in FIG. 2 in the open or break position wherein the contacts 24a are spaced from the plug prongs 16, 17 and 18. The contacts are urged into this position because the flexible arms 24 are inherently biased to assume this position. The contact actuator 46 is spaced downwardly from the flexible contact arms, being urged in this position by the coil spring 48. The three ribs 46b on the lower portion 46a of the actuator are positioned in the full grooves 52 of the guide 40 as may be seen in FIG. 5. The slider 42 has been pushed downwardly by the spring 48 and the actuator 46' to the lower portion of the guide 40 as seen in FIG. 2. Movement in this direction is limited by the solenoid plunger 34 and the reset button 66. This condition is schematically shown in full lines in FIG. 9. As can be seen, the lower ends 46c of the actuator 46b are engaging the upper angled surfaces 420 of three of the ribs on the slider.

If it is desirable to close the switch contacts to make an electrical connection between the plug prongs and the power cord, it is necessary to move the solenoid plunger 34 upwardly. This is accomplished by depressing the reset button 66 to the position shown in FIG. 7. Alternatively, the solenoid plunger 34 may be moved axially by energizing the solenoid coil 26, which may be accomplished by a separate power source and separate external connections (not shown) connected to the solenoid coil. Various automatic switching arrangements may be employed to automatically close the plug contacts.

Axial upward movement of the solenoid plunger 34 raises the slider 42 upwardly with its ribs 42b sliding within the guide grooves 52 and 54. The slider in turn pushes the actuator 46 upwardly against the urging of the compression spring 48. When the slider 42 is raised to the position where its rib and end cam surfaces 420 become aligned in the same plane with the ends or cam surfaces 50a of the guide ribs 50, the actuator ribs 46b are pushed out of the guide slots 52 where the rib cam surfaces 460 become aligned in the same plane with the cam surfaces 50a of the ribs 50. Because of the cam surfaces on the ribs 42b, 46b and 50 and because of the continual urging of the spring 48, the lower ends of the ribs 461; are urged to slide to the right or in a counterclockwise direction as viewed in FIGS. 3, 9 and 10. This in turn rotates the actuator in that direction. The cam surfaces 46c on the lower end of the ribs 46b first slide onto the cam surfaces 500 on the guide ribs 50,

thus leaving engagement with the slider ribs. The cam surfaces 460 continue to slide beyond the cam surfaces 50a on the guide ribs 50 and onto the cam surfaces 54a of the guide structure defining the ends of the shallow grooves 54. The initial part of this sliding movement is shown in phantom lines in FIG. and the end position is shown in full lines in FIG. 10. In this position the actuator wants to rotate further because of the cam surfaces 54a. However, the upper side edges of the next guide ribs 50 prevent further movement. The actuator is thus held radially and axially.

Consider now what has occurred with respect to the actuator 46, the contact arms 24 and the contacts 24a in relation to the plug prongs during this movement. Initially each contact arm 24 is axially aligned with the intersection between a flat 63 and the lower end of a ramp 62, as in FIG. 9. As the actuator is moved to its uppermost position. the actuator engages the contact arms 24' as seen in broken lines in FIG. 9; but the contacts 24a remain spaced from the plug prongs. As the actuator rotates to the broken line position of FIG. 10, the flexible arms move up the ramps 62, as indicated by 24", while the entire actuator is moving downwardly. The actuator continues to rotate a total of 60 into the locked position at the end of the shallow grooves. The arms 24 are moved up by the ramps more than the actuator moves down. That is, the ramp axial height is greater than the distance between the lower end of the cam surface 426 and the high end of the cam surface 50a. Thus the contacts 24a engage the-plug prongs while the arms 24 move up the ramps 62. Note from the solid line position of FIG. 10, that the peak of the ramps 62 engage the contact arms 24" at about their midpoint in the final on position.

Now, if a dangerous condition should occur in connection with the electrical appliance energized through the power cord 30 and the safety plug of the invention, such as current being advertently applied to the ground line, the solenoid coil is immediately energized, being connected in series in the ground line. This causes the solenoid plunger 34 to move upwardly, once more operating the actuator mechanism.

More specifically, the slider moves axially and lifts the actuator out of its locked position at the ends of the shallow grooves. The contact arms 24 are thus momentarily raised further to the upper broken line position shown in FIG. 10 as 24". This actuator position is like the broken line position of FIG. 9 only shifted to the right. The contacts 24a being in contact with the plug prongs at the start of the movement cannot move upwardly, but the flexibility of the contact arms accommodate such movement. If desired, the guide ribs 50 which hold the actuator rotationally may be shortened so that they still hold the actuator but would result in less flexing of the contact arms 24. The guide would then have to be properly oriented with respect to the contact arms.

Upon reaching the end of the guide ribs 50, the actuator is free to rotate onto the cam surfaces under the urging of the spring 48. After rotating the actuator about 15 the ribs 46b would be in position to engage a valley in the upper surface of the slider 42b, if the solenoid coil were still energized, holding the slider in its upper position. However, after 15 rotation of the actuator, the ramps 62 are moved out from under the contact arms so that they move away from the plug prongs into engagement with a flat 63, as shown in the lower broken line position of FIG. 10 as 24". The actuator position is like the broken line showing of FIG. 10 only shifted 60 to the right. All power through the plug is now interrupted. The actuator continues to rotate another 45 until the actuator ribs slide into the full grooves 50, which is the full line position of FIGS. 9 and 2 wherein the actuator is widely spaced from the plug contacts and all force is removed from the contact arms. When the plug is to be once more energized, further axial movement of the solenoid plunger 34 by the reset button or an external power supply will once more move the axtuator to the switch closed position.

Thus it can be seen that stepped off-and-on switch operation is easily obtained with the device illustrated. Advantageously the components of the device may be mass produced very economically such that a low cost but reliably operating device is obtained. Consequently, it is practical to make such devices available for all electrical appliances either as part of the power cord in place of a conventional plug or as a separate electrical device to which a conventional plug could connect.

What is claimed is:

I. An electrical device comprising a plurality of electrical conductors;

switch means connected to one or more of said conductors;

a solenoid coil connected to be energized by a predetermined current through one of said conductors, and a solenoid plunger within the coil, axially movable upon energization of the coil from an initial position to an extended position;

an actuator mounted to be rotated adjacent said switch means for operating said switch means;

means positioned between the plunger and said actuator for cooperating with the actuator to convert the axial movement of said plunger into stepped rotary movement of said actuator; and

means for maintaining the selected switch position after the solenoid plunger has been extended and returned to its initial position.

2. The safety device of claim 1 wherein said converting and maintaining means include a fixed tubular guide having a plurality of axially extending, circumferentially spaced ribs formed on its inner surface and a plurality of grooves formed between said ribs, the upper ends of said ribs having angled cam surfaces formed thereon, a slider positioned within said guide having a purality of ribs which fit within the guide slots so that the slider can be axially moved within the guide but is rotationally restrained, the upper ends of the slider ribs having cam surfaces on the same angle as the cam surfaces on the guide ribs, and whereas said actuator has a portion with a plurality of axially extending ribs which fit within the upper end of the guide grooves, the lower ends of said actuator ribs having cam surface which mate with the cam surfaces on the slider and the guide, said cam surfaces being arranged such that axial movement of said slider caused by said solenoid plunger will move the actuator axially to align the cams allowing the actuator to rotate on the cam surfaces from one position wherein the switch means is closed to a second position wherein the switch means is open.

3. The safety device of claim 2 wherein said guide grooves include a plurality of grooves which extend to the base of the guide ribs and a plurality of grooves which extend only a portion of the way to the base of the guide ribs thus creating a series of shallow grooves and a series of deep grooves, said grooves being spaced by said guide ribs and being arranged alternately so that the shallow grooves are in between the deep grooves, the upper end of the shallow grooves being angled to form continuations of the cam surfaces of one of the adjacent guide ribs, such that when the actuator is in the switch closed position the actuator ribs are engaging the cam surfaces of the ends of the shallow grooves in the guide and when the switch means is in the open position the actuator ribs are positioned within the deep grooves in the guide.

4. An electrical safety plug comprising:

a housing;

three plug prongs supported by the housing and extending outwardly therefrom including hot, common, and ground prongs;

a three wire power cord extending into the housing;

conductor means within the housing for connecting each of the plug prongs to the respective one of the wires within the power cord including one or more flexible contact arms positioned to cooperate with a respective one of said prongs;

a solenoid coil positioned in the housing connected to be energized by a predetermined current through one of said wires;

a solenoid plunger within said coil which is axially movable upon energization of the coil; and

means responsive to the axial movement of the solenoid plunger for controlling the engagement of said contact arms with said plug prongs including a generally circular actuator having an upper surface formed with a series of sawtooth cam surfaces for engagement with said contact arms, a spring urging said actuator away from said contact arms, and means for converting the axial movement of said solenoid plunger into step-like rotational movement of said actuator.

5. The safety plug of claim 4 wherein said responsive means further includes a tubular guide supported by said housing having a plurality of axially extending, circumferentially spaced ribs formed on its inner surface and a plurality of grooves formed between said ribs, the upper ends of said ribs having cam surfaces formed thereon, a slider positioned within said guide having a plurality of ribs which fit within the guide slots so that the slider can be axially moved within the guide but is rotationally restrained, the upper ends of the slider ribs having cam surfaces on the same angle as the cam surfaces on the guide ribs, said actuator having a lower portion with a plurality of axially extending ribs which fit within the upper end of the guide grooves, the lower ends of said actuator ribs having cam surfaces which mate with the cam surfaces on the slider and the guide, said cam surfaces being arranged such that axial movement of said slider caused by said solenoid plunger will rotate said actuator from one position wherein the switch contact arms are held in engagement with the plug prongs by the actuator to a second position wherein the actuator does not hold the contacts in engagement with the plug prongs.

6. The safety plug of claim 5 wherein said guide grooves include a plurality of grooves which extend to the base of the guide ribs and a plurality of grooves which extend only a portion of the way to the base of the guide ribs thus creating a series of shallow grooves and a series of deep grooves, said grooves being spaced by said guide ribs and being arranged alternately so that the shallow grooves are in between the deep grooves, the upper end of the shallow grooves being angled to form continuations of the cam surfaces of one of the adjacent guide ribs, such that when the actuator is holding the switch contact arms in the closed position, the actuator ribs are engaging the cam surfaces of the ends of the shallow grooves in the guide and when the contact arms are in the open position the actuator ribs are positioned within the deep grooves in the guide.

7. The safety plug of claim 6 wherein the guide has six ribs, three deep grooves and three shallow grooves, said slider has six ribs which fit within the six guide grooves, and said actuator has three ribs equal in circumferential width to the guide ribs, and the upper portion of the actuator includes a series of three equally" spaced ramps for engaging the contacts, whereby said actuator is rotated in sixty degree steps gy a single reciprocation of the slider and the solenoid plunger.

8. An electrical safety plug comprising;

a housing;

three plug prongs supported by the housing and extending outwardly therefrom including hot, common, and ground prongs;

a three wire power cord extending into the housing;

conductor means within the housing for connection each of the plug prongs to the respective one of the wires within the power cord including one or more flexible contact arms positioned to cooperate with a respective one of said prongs;

a solenoid coil positioned in the housing connected to be energized bya predetermined current through one of said wires;

a solenoid plunger within said coil which is axially movable upon energization of the coil; and

means responsive to the axial movement of the solenoid plunger for controlling the engagement of said contact arms with said plug prongs;

the conductor means joining the contact arms to the power cords being rigid members which are spaced circumferentially in the housing and extend axially within the housing, and said solenoid and the means responsive to the solenoid being confined within the housing spaced inwardly from said conductors.

9. An electrical safety plug comprising:

a housing;

three plug prongs supported by the housing and extending outwardly therefrom including hot, common, and ground prongs,

a three wire power cord extending into the housing;

conductor means within the housing for connecting each of the plug prongs to the respective one of the wires within the power cord including one or more flexible contact arms positioned to cooperate with a respective one of said prongs;

a solenoid coil positioned in the housing connected to be energized by a predetermined current through one of said wires;

a solenoid plunger within said coil which is axially movable upon energization of the coil;

means responsive to the axial movement of the solenoid plunger for controlling the engagement of said contact arms with said plug prongs; and

a reset button extending into said housing adjacent the power cord for manually reciprocating the solenoid plunger to operate the mechanism responsive to the solenoid in a manner to open the switch contact arms.

10. An electrical safety plug comprising:

a generally cylindrical housing;

three plug prongs supported by and extending outwardly from one end of the housing including hot, common, and ground prongs;

three circumferentially spaced conductors axially extending through adjacent the periphery of the housing;

three flexible switch contact arms each attached to a respective one of said conductors and extending inwardly to cooperate with a respective one of said prongs, said contact arms being normally spaced and biased away from the prongs;

a three wire powere cord extending through the other end of the housing with the wires respectively connected to said three conductors;

a solenoid coil positioned in the housing and connected in series between the ground conductor and the ground wire in the power cord;

a solenoid core plunger positioned within the coil and extending axially in the housing;

a manual reset button accessible from the exterior of the housing and engaging one end of said plunger;

means responsive to axial movement of said plunger to close said contact arms including: an axially extending tubular guide supported within 10 the housing with one end adjacent the solenoid coil and plunger and the other end spaced from said switch contact arms, said guide inner surface having six axially extending, circumferentially spaced ribs separating six axially extending grooves, with three of the grooves being equally spaced from each other and extending axially completely through the guide, and the other three grooves being radially as deep as the first mentioned three at the guide end closest to the contact arms and being radially shallower through the rest of the guide, the ends of said guide ribs spacing the grooves extending at a common angle with respect to a radial plane through the guide, and the ends of the guide structure forming the shallow grooves extending at the same angle as the rib ends and forming a continuation of the cam surface on one adjacent rib end whereby the ends of said adjacent rib and the ends of the adjacent shallow grooves form a series of cam surfaces which are bounded on the rib side by a deep groove and on the shallow groove side are bounded by another one of said ribs;

a slider positioned within said guide having a series of circumferentially spaced ribs extending into the guide grooves to enable the slider to slide axially within the guide while being rotationally restrained, the lower end of the slider being engaged by said plunger, the upper ends of the slider ribs having a cam surface formed with the same angle as the ends of the guide ribs; and

an actuator having a first portion with three cirspring means urging said actuator away from said 

1. An electrical device comprising a plurality of electrical conductors; switch means connected to one or more of said conductors; a solenoid coil connected to be energized by a predetermined current through one of said conductors, and a solenoid plunger within the coil, axially movable upon energization of the coil from an initial position to an extended position; an actuator mounted to be rotated adjacent said switch means for operating said switch means; means positioned between the plunger and said actuator for cooperating with the actuator to convert the axial movement of said plunger into stepped rotary movement of said actuator; and means for maintaining the selected switch position after the solenoid plunger has been extended and returned to its initial position.
 2. The safety device of claim 1 wherein said converting and maintaining means include a fixed tubular guide having a plurality of axially extending, circumferentially spaced ribs formed on its inner surface and a plurality of grooves formed between said ribs, the upper ends of said ribs having angled cam surfaces formed thereon, a slider positioned within said guide having a purality of ribs which fit within the guide slots so that the slider can be axially moved within the guide but is rotationally restrained, the upper ends of the slider ribs having cam surfaces on the same angle as the cam surfaces on the guide ribs, and whereas said actuator has a portion with a plurality of axially extending ribs which fit within the upper end of the guide grooves, the lower ends of said actuator ribs having cam surface which mate with the cam surfaces on the slider and the guide, said cam surfaces being arranged such that axial movement of said slider caused by said solenoid plunger will move the actuator axially to align the cams allowing the actuator to rotate on the cam surfaces from one position wherein the switch means is closed to a second position wherein the switch means is open.
 3. The safety device of claim 2 wherein said guide grooves include a plurality of grooves which extend to the base of the guide ribs and a plurality of grooves which extend only a portion of the way to the base of the guide ribs thus creating a series of shallow grooves and a series of deep grooves, said grooves being spaced by said guide ribs and being arranged alternately so that the shallow grooves are in between the deep grooves, the upper end of the shallow grooves being angled to form continuations of the cam surfaces of one of the adjacent guide ribs, such that when the actuator is in the switch closed position the actuator ribs are engaging the cam surfaces of the ends of the shallow grooves in the guide and when the switch means is in the open position the actuator ribs are positioned within the deep grooves in the guide.
 4. An electrical safety plug comprisiNg: a housing; three plug prongs supported by the housing and extending outwardly therefrom including hot, common, and ground prongs; a three wire power cord extending into the housing; conductor means within the housing for connecting each of the plug prongs to the respective one of the wires within the power cord including one or more flexible contact arms positioned to cooperate with a respective one of said prongs; a solenoid coil positioned in the housing connected to be energized by a predetermined current through one of said wires; a solenoid plunger within said coil which is axially movable upon energization of the coil; and means responsive to the axial movement of the solenoid plunger for controlling the engagement of said contact arms with said plug prongs including a generally circular actuator having an upper surface formed with a series of sawtooth cam surfaces for engagement with said contact arms, a spring urging said actuator away from said contact arms, and means for converting the axial movement of said solenoid plunger into step-like rotational movement of said actuator.
 5. The safety plug of claim 4 wherein said responsive means further includes a tubular guide supported by said housing having a plurality of axially extending, circumferentially spaced ribs formed on its inner surface and a plurality of grooves formed between said ribs, the upper ends of said ribs having cam surfaces formed thereon, a slider positioned within said guide having a plurality of ribs which fit within the guide slots so that the slider can be axially moved within the guide but is rotationally restrained, the upper ends of the slider ribs having cam surfaces on the same angle as the cam surfaces on the guide ribs, said actuator having a lower portion with a plurality of axially extending ribs which fit within the upper end of the guide grooves, the lower ends of said actuator ribs having cam surfaces which mate with the cam surfaces on the slider and the guide, said cam surfaces being arranged such that axial movement of said slider caused by said solenoid plunger will rotate said actuator from one position wherein the switch contact arms are held in engagement with the plug prongs by the actuator to a second position wherein the actuator does not hold the contacts in engagement with the plug prongs.
 6. The safety plug of claim 5 wherein said guide grooves include a plurality of grooves which extend to the base of the guide ribs and a plurality of grooves which extend only a portion of the way to the base of the guide ribs thus creating a series of shallow grooves and a series of deep grooves, said grooves being spaced by said guide ribs and being arranged alternately so that the shallow grooves are in between the deep grooves, the upper end of the shallow grooves being angled to form continuations of the cam surfaces of one of the adjacent guide ribs, such that when the actuator is holding the switch contact arms in the closed position, the actuator ribs are engaging the cam surfaces of the ends of the shallow grooves in the guide and when the contact arms are in the open position the actuator ribs are positioned within the deep grooves in the guide.
 7. The safety plug of claim 6 wherein the guide has six ribs, three deep grooves and three shallow grooves, said slider has six ribs which fit within the six guide grooves, and said actuator has three ribs equal in circumferential width to the guide ribs, and the upper portion of the actuator includes a series of three equally spaced ramps for engaging the contacts, whereby said actuator is rotated in sixty degree steps gy a single reciprocation of the slider and the solenoid plunger.
 8. An electrical safety plug comprising: a housing; three plug prongs supported by the housing and extending outwardly therefrom including hot, common, and ground prongs; a three wire power cord extending into the housing; conductor means within the housing for connection each of the Plug prongs to the respective one of the wires within the power cord including one or more flexible contact arms positioned to cooperate with a respective one of said prongs; a solenoid coil positioned in the housing connected to be energized bya predetermined current through one of said wires; a solenoid plunger within said coil which is axially movable upon energization of the coil; and means responsive to the axial movement of the solenoid plunger for controlling the engagement of said contact arms with said plug prongs; the conductor means joining the contact arms to the power cords being rigid members which are spaced circumferentially in the housing and extend axially within the housing, and said solenoid and the means responsive to the solenoid being confined within the housing spaced inwardly from said conductors.
 9. An electrical safety plug comprising: a housing; three plug prongs supported by the housing and extending outwardly therefrom including hot, common, and ground prongs, a three wire power cord extending into the housing; conductor means within the housing for connecting each of the plug prongs to the respective one of the wires within the power cord including one or more flexible contact arms positioned to cooperate with a respective one of said prongs; a solenoid coil positioned in the housing connected to be energized by a predetermined current through one of said wires; a solenoid plunger within said coil which is axially movable upon energization of the coil; means responsive to the axial movement of the solenoid plunger for controlling the engagement of said contact arms with said plug prongs; and a reset button extending into said housing adjacent the power cord for manually reciprocating the solenoid plunger to operate the mechanism responsive to the solenoid in a manner to open the switch contact arms.
 10. An electrical safety plug comprising: a generally cylindrical housing; three plug prongs supported by and extending outwardly from one end of the housing including hot, common, and ground prongs; three circumferentially spaced conductors axially extending through adjacent the periphery of the housing; three flexible switch contact arms each attached to a respective one of said conductors and extending inwardly to cooperate with a respective one of said prongs, said contact arms being normally spaced and biased away from the prongs; a three wire powere cord extending through the other end of the housing with the wires respectively connected to said three conductors; a solenoid coil positioned in the housing and connected in series between the ground conductor and the ground wire in the power cord; a solenoid core plunger positioned within the coil and extending axially in the housing; a manual reset button accessible from the exterior of the housing and engaging one end of said plunger; means responsive to axial movement of said plunger to close said contact arms including: an axially extending tubular guide supported within the housing with one end adjacent the solenoid coil and plunger and the other end spaced from said switch contact arms, said guide inner surface having six axially extending, circumferentially spaced ribs separating six axially extending grooves, with three of the grooves being equally spaced from each other and extending axially completely through the guide, and the other three grooves being radially as deep as the first mentioned three at the guide end closest to the contact arms and being radially shallower through the rest of the guide, the ends of said guide ribs spacing the grooves extending at a common angle with respect to a radial plane through the guide, and the ends of the guide structure forming the shallow grooves extending at the same angle as the rib ends and forming a continuation of the cam surface on one adjacent rib end whereby the ends of said adjacent rib and the ends of the adjacent shallow grooves form a series of cam surfaces which are bounded on the rib side by a deep groove and on the shallow groove side are bounded by another one of said ribs; a slider positioned within said guide having a series of circumferentially spaced ribs extending into the guide grooves to enable the slider to slide axially within the guide while being rotationally restrained, the lower end of the slider being engaged by said plunger, the upper ends of the slider ribs having a cam surface formed with the same angle as the ends of the guide ribs; and an actuator having a first portion with three circumferentially spaced ribs sized and spaced to fit within the full grooves in said guide, the lower ends of the actuator ribs facing the guide being angled to form a cam surface which mates with the cam surfaces on the guide and the slider, said actuator having a second portion including a series of ramps being arranged so that the contact arms are held by said ramps in engagement with said plug prongs when the actuator ribs are engaging the cam surfaces on the ends of said shallow grooves in said guide; and spring means urging said actuator away from said contact arms. 